The present application relates generally to hand operated torque wrenches and, more particularly, to torque wrenches with the ability of selecting a torque value from a finite plurality of preset values.
Torque wrenches are generally used by workers to ensure that the correct amount of torque is applied to a fastener or other torqueable device. Threaded fasteners and the like are frequently used in torque-sensitive applications, thus making it imperative that the correct amount of torque is applied. Otherwise, fatigue failure, thread stripping, damage to fastened parts, and the like, can result.
Torque wrenches, either mechanical or electronic, typically combine a wrench head, such as a ratcheting-type head with a drive lug extension, a lever, a handle, and a torque-responsive mechanism which typically conveys an audible, visible or tactile response once a desired amount of torque has been applied and/or provides an indication of the amount of torque applied.
Such torque wrenches are generally of two types—preset (or fixed) and adjustable. Preset torque wrenches provide an indication when a single, fixed amount of torque is reached with no ability for the user to modify the preset, fixed torque value. Preset torque wrenches are generally preferred in areas where, for example, a manufacturer designates a specific amount of torque for sensitive, often repetitive, applications. To ensure that the user meets such torque specifications, a fixed, nonadjustable preset torque wrench is preferred. However, the usability of such a torque wrench is limited because it can only be used for the single, fixed torque value, thus requiring the user to maintain a plurality of different preset torque wrenches if, for example, a certain machine requires differing amounts of torque for different fasteners.
Adjustable torque wrenches, on the other hand, allow the user to incrementally modify the torque value, for example between 20–200 ft-lbs. A selector mechanism may be provided, generally with a graduated torque value scale, such as a micrometer-type scale, to allow the user to approximately select the desired output torque value, whereupon the torque-responsive mechanism is accordingly adjusted. The scope of use of such torque wrenches is greater than fixed, preset torque wrenches because the ability of varying the torque value allows use on many different torque sensitive applications. However, potential user error in selecting the correct torque amount for a certain task is greatly increased due to misreading or inherent inaccuracies of the selector or accidental movement of the selector from the desired torque value.